Fair Value Measurements - Changes in level 3 recurring fair value measurements, assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Jan. 01, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 28,695	$ 29,622	$ 28,647	$ 31,627
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	126	64	251	265
Other Comprehensive Income (Loss)	(392)	(936)	(19)	(3,601)
Purchases, Sales, Issuances and Settlements, Net	347	(42)	1,124	1,201
Gross Transfers In	841	2,217	1,359	4,414
Gross Transfers Out	(311)	(571)	(2,143)	(3,552)
Other	107	0	194	0
Fair Value End of Period	29,413	30,354	29,413	30,354
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(13)	(90)	(123)	(140)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ (440)	$ (868)	$ (308)	$ (2,835)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss
Gross Transfers Out			$ 0
Market risk benefit assets, at fair value	$ 978		$ 978		$ 796	$ 338	$ 338
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues		Revenues
Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	$ 978		$ 978		796
Level 3 | Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	$ 978	$ 743	$ 978	$ 743	$ 796
Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total net realized gains (losses)	Total net realized gains (losses)	Total net realized gains (losses)	Total net realized gains (losses)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total net realized gains (losses)	Total net realized gains (losses)	Total net realized gains (losses)	Total net realized gains (losses)
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 24,980	$ 24,368	$ 24,899	$ 26,862
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	141	43	300	273
Other Comprehensive Income (Loss)	(380)	(911)	(14)	(3,549)
Purchases, Sales, Issuances and Settlements, Net	239	61	845	853
Gross Transfers In	796	2,162	1,300	4,027
Gross Transfers Out	(296)	(513)	(1,884)	(3,256)
Other	81	0	115	0
Fair Value End of Period	25,561	25,210	25,561	25,210
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(440)	(868)	(308)	(2,835)
Bonds available for sale | Obligations of states, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	869	957	824	1,431
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(1)	(2)	1
Other Comprehensive Income (Loss)	(78)	(106)	(26)	(534)
Purchases, Sales, Issuances and Settlements, Net	(23)	(29)	(31)	(94)
Gross Transfers In	0	0	0	17
Gross Transfers Out	0	(7)	0	(7)
Other	0	0	0	0
Fair Value End of Period	765	814	765	814
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(82)	(167)	(54)	(319)
Bonds available for sale | Non-U.S. governments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	6	9	1	7
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	0	1	0
Other Comprehensive Income (Loss)	0	0	1	0
Purchases, Sales, Issuances and Settlements, Net	(3)	(1)	(5)	(1)
Gross Transfers In	0	1	7	3
Gross Transfers Out	0	0	(2)	0
Other	0	0	0	0
Fair Value End of Period	3	9	3	9
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	1	0
Bonds available for sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,721	2,483	2,847	2,641
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(5)	(31)	(101)	(57)
Other Comprehensive Income (Loss)	(78)	(53)	(19)	(204)
Purchases, Sales, Issuances and Settlements, Net	(76)	(100)	(450)	(137)
Gross Transfers In	176	1,781	496	2,163
Gross Transfers Out	(200)	(163)	(1,219)	(489)
Other	0	0	(16)	0
Fair Value End of Period	1,538	3,917	1,538	3,917
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(83)	(55)	(61)	(183)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	7,617	8,352	7,553	10,378
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	101	101	315	323
Other Comprehensive Income (Loss)	(82)	(267)	37	(1,210)
Purchases, Sales, Issuances and Settlements, Net	(74)	(299)	(275)	(1,173)
Gross Transfers In	2	2	33	2
Gross Transfers Out	(25)	(8)	(89)	(439)
Other	7	0	(28)	0
Fair Value End of Period	7,546	7,881	7,546	7,881
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(122)	(39)	(33)	(704)
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	553	871	926	1,190
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(1)	(25)	12
Other Comprehensive Income (Loss)	(27)	(31)	(69)	(144)
Purchases, Sales, Issuances and Settlements, Net	4	(33)	(35)	84
Gross Transfers In	65	12	98	12
Gross Transfers Out	(25)	(12)	(328)	(348)
Other	0	0	0	0
Fair Value End of Period	567	806	567	806
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(32)	(50)	(114)	(143)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	14,214	11,696	12,748	11,215
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	51	(25)	112	(6)
Other Comprehensive Income (Loss)	(115)	(454)	62	(1,457)
Purchases, Sales, Issuances and Settlements, Net	411	523	1,641	2,174
Gross Transfers In	553	366	666	1,830
Gross Transfers Out	(46)	(323)	(246)	(1,973)
Other	74	0	159	0
Fair Value End of Period	15,142	11,783	15,142	11,783
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(121)	(557)	(47)	(1,486)
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,392	3,127	1,527	2,697
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(40)	32	(314)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	40	(66)	49	424
Gross Transfers In	1	40	5	325
Gross Transfers Out	(3)	(16)	(239)	(87)
Other	26	0	79	0
Fair Value End of Period	1,453	3,045	1,453	3,045
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(14)	(110)	(41)	(456)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | Obligations of states, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	3		0
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0		0
Other Comprehensive Income (Loss)	0		0
Purchases, Sales, Issuances and Settlements, Net	(2)		1
Gross Transfers In	0		0
Gross Transfers Out	0		0
Other	0		0
Fair Value End of Period	1		1
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0		0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0		0
Other bond securities | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	155	461	416	134
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	1	(5)	3	(9)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	65	66	(7)	190
Gross Transfers In	0	28	0	250
Gross Transfers Out	0	(1)	(191)	(16)
Other	0	0	0	0
Fair Value End of Period	221	549	221	549
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	(7)	2	(8)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	164	192	173	196
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(2)	(7)	5	(25)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(4)	26	(20)	40
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	158	211	158	211
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(3)	(8)	(8)	(28)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	26	32	28	35
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(3)	(5)	(6)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	0
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	23	29	23	29
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(3)	(3)	(4)	(6)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,044	2,442	910	2,332
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	1	(25)	29	(274)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(19)	(158)	75	194
Gross Transfers In	1	12	5	75
Gross Transfers Out	(3)	(15)	(48)	(71)
Other	26	0	79	0
Fair Value End of Period	1,050	2,256	1,050	2,256
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(11)	(92)	(31)	(414)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	72	12	39	6
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	1	(1)	3	(1)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(2)	8	27	14
Gross Transfers In	0	15	10	15
Gross Transfers Out	(12)	0	(20)	0
Other	0	0	0	0
Fair Value End of Period	59	34	59	34
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	0	2	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,140	2,008	2,075	1,948
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(13)	62	(84)	307
Other Comprehensive Income (Loss)	(12)	(25)	(5)	(52)
Purchases, Sales, Issuances and Settlements, Net	69	(45)	198	(83)
Gross Transfers In	44	0	44	47
Gross Transfers Out	0	(42)	0	(209)
Other	0	0	0	0
Fair Value End of Period	2,228	1,958	2,228	1,958
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	20	(84)	316
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	111	107	107	114
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	1	0	5	(7)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	112	107	112	107
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 0	$ 0	$ 0	$ 0